Chromium-vanadium-iron alloy cutting tool



Patented Oct. 6, 1942 I CHROMIUM-VANADIUM-IRON ALLUY- CUTTING TOOLCharles 0. Burgess and William D. Forgeng, Niagara Falls, N. Y.,assignors to Haynes Stellite Company, a corporation of Indiana NoDrawing. Application July 30, 1940, Serial No. MBAM 2 Claims.

ment, it has been possible to vary the hardness.

toughness, and strength of the alloys over wide ranges. But hardness ofa very high degree such as is required of a metal-cutting tool hasheretofore been accompanied by an undue degree of brittleness. Cuttingtool high speed" steels have been basically tungsten-iron compositionsrather than chromium-iron, and have typically contained 18% tungsten, 4%chromium, and 1% vanadium (so-called 18-4l) sometimes modihad by theaddition of one or more of the metals cobalt, nickel and molybdenum.

It is a primary object of the invention to provide an abrasion resistantchromium iron alloy cutting tool which will cut metals at high speeds atleast as well as 18-4-1 high speed steel.

We have discovered that the properties of a hard chromium-iron alloycontaining between 25% and 60% chromium are considerably enhanced by theaddition of carbon, preferably in a percentage between 1% and 3%, and ofat least 5% vanadium, the sum of the percentages of chromium andvanadium being between 35% and 70%. For some purposes, the carboncontent may be somewhat below or abov the range of 1% to 3%. We havefurther found that such an alloy may be heat treated to improve itsproperties as a cutting tool or other a rasion-reslstant article. Wehave also found tha the toughness and general suitability of such analloy for use as a cutting tool and other abrasion-resisting articlesmay be still further enhanced by the addition of one or more of thefollowing elements: cobalt, nickel, boron, silicon tungsten, columbium,tantalum, and molybdenum, in certain pro portions hereinafter described.

Mor specifically, according to the invention abrasion-resistant cuttingtools comprise chromium between 25% and 60%, at least 5% vanadium (thesum of the chromium andvanaclium being between 35% and 70%), at least15% iron, and carbon, the carbon preferably being between 1 and 3%.

In addition to the chromium, vanadium, iron, and carbon, the alloy maycontain up to 5% silicon or up to 5% boron, or both in an aggregateproportion not exceeding 5%; up to nickel; up to 10% cobalt; and a totalof up to 10% of one or more of the elements tungsten, molybdenum,columbium, tantalum, titanium, and zirconium. Small fractionalpercentages of the common impurities, such as sulfur, phosphorus, andnitrogen, may also be present. Preferably, the carbon does not exceed2.5%

The tools are heated at temperatures within the range of 550 C. and 850C. for a time be-- tween about 5 minutes at the higher temperatureswithin said range and about twenty hours at the lower temperatures. Thedescribed heat treatment markedly improves the utility of thecomposition throughout the range described.

Although this invention does not depend for its successful applicationon any theory, we believe that the improvement is at least partlybrought about by the formation of a constituent known as the sigmaphase, a phase described in the literature variously as an intermetalliccompound and as a highly saturated solid solution in an unusualallotropic form of iron.

A limited amount of hot forging may be done on most of the alloycompositions of the invention if they are not previously given aprolonged'exposure to elevated temperatures below 900 C. Preferably,forging is commenced before the cast metal has cooled from the castingstep to below 900 C.

Depending chiefly upon the composition and the heat treating conditions,the hardness of the alloy tool of invention varies between'theapproximate limits or' to Rockwell C. The transverse strength of theas-cast alloy is upwards of 700 pounds (loading applied centrally to asection 0.5 inch by 0.5 inch square, supported in a a inch span), andusually attains i pounds and sometimes more.

Cutting tests indicate that the alloy tool of the invention comparesfavorably with standard high speed steel tools of the 18-14-1 type. Inaccelerated life tests cutting steel billets and semi-steel billets,using surface speeds, feeds, and cuts considerably greater than normal,tools of this invention cut from two to eight times as far as standardRex AAA, a widely used high speed steel of high quality.

We claim:

l. A cutting tool having substantially the composition: between 25%and60% chromium, at

least 5% vanadium, the sum of the chromium and vanadium being between35% and 70%,

within the range of 550 C. to 850 C. for a time between five minutes andtwenty hours.

2. A cutting tool having substantially the composition: between 2 5% and60% chromium, at least 5% vanadium, the sum 01' the chromium andvanadium being between 35% and 70%, be-

tween 1% and 2.5% carbon, remainder iron;

which tool is in the improved condition resulting from subjection toheating within the range 0! 550 C. to 850 C. for a time between fiveminutes and twenty hours.

CHARLES O. BURGESS. WILLIAM D. FORGENG.

